Rectifier circuit including a self-clamping transistor

ABSTRACT

A rectifier circuit is described, which includes a cathode terminal, an anode terminal and, between the cathode terminal and the anode terminal, an electronic circuit which includes at least one MOSFET transistor including an integrated inverse diode, the drain-source breakdown voltage of the MOSFET transistor operated in the avalanche mode corresponding to the clamping voltage between the cathode terminal and the anode terminal of the rectifier circuit. In addition, a method is provided for operating a rectifier circuit which contains a cathode terminal, an anode terminal and, between the cathode terminal and the anode terminal, at least one MOSFET transistor including an integrated inverse diode, the drain-source breakdown voltage of the MOSFET transistor being selected in accordance with the clamping voltage between the cathode terminal and the anode terminal, and the MOSFET transistor being operated in the avalanche mode.

FIELD

The present invention relates to a rectifier circuit, an electroniccomponent including a rectifier circuit, a generator for the voltagesupply of a motor vehicle including a rectifier circuit, and a methodfor operating a rectifier circuit.

BACKGROUND INFORMATION

In order to generate DC voltages from AC voltages, rectifier bridgesmade up of an interconnection of diodes are mostly utilized at present.Alternatively, synchronous rectifiers or active rectifiers may beutilized instead of diodes, in order to reduce the conducting statepower losses. In this case, suitable power MOSFETs replace the diodeswhich are usually utilized. This results in greater circuit complexity,since precise control with respect to time is necessary for the MOSFETs.Such additional circuitry parts are mostly combined in integratedcircuits and are connected to the particular gate terminals of theMOSFETs.

A simple variant of a synchronous rectifier is described in GermanPatent Application No. DE 10 2007 060 219 A1. Therein, the additionalcircuit elements are individually assigned to each power MOSFET. Theadditional circuit elements are each supplied with current by a smallbackup capacitor in this case. If the additional circuit elements, whichare composed of transistors, diodes, resistors, and the backupcapacitor, are integrated together with the power MOSFET into a smallhousing, the component formed in this way is interconnectable like adiode.

Circuit arrangements of this type may also be designed in such a waythat they allow for a limitation of high voltage peaks. High voltagepeaks occur, for example, when large, sudden load changes occur in an ACgenerator. Such a generator may be, for example, a 3-phase or multiphasemotor vehicle generator. Such a brief operating condition is referred toas a load dump.

FIG. 1 from German Patent Application No. DE 10 2007 060 219 A1 shows arectifier circuit which is utilized instead of a silicon PN diode in arectifier bridge. It includes not only a silicon PN diode but also acathode terminal K1 and an anode terminal A1. MOS transistor T1 andinverse diode D6 are connected in parallel and, together in thisinterconnection, technically form a microelectronic component.

The rectifier circuit includes a symmetrically configured differentialamplifier which is formed by transistors T2 and T3 and resistors R1, R2and R3. A first input of this differential amplifier is connected via adiode D1 to cathode terminal K1 and to drain terminal of MOS transistorT1. A second input of this differential amplifier is connected via adiode D2 to anode terminal A1. This differential amplifier amplifies thepotential difference between cathode terminal K1 and anode terminal A1of the rectifier circuit. Due to the symmetrical configuration of thedifferential amplifier, temperature differences and aging effects haveonly a slight effect on the properties of the differential amplifier.

The output signal from the differential amplifier is available at thecollector of transistor T3 and is relayed via a resistor R4 to the inputof a current amplifier stage. This current amplifier stage is made up oftransistors T4 and T5, the bases of which are interconnected. Zenerdiode D5 acts as a protective element for transistor T1 and protects itsgate against overvoltages.

When an AC voltage is rectified, an AC voltage having frequency f ispresent between cathode terminal K1 and anode terminal A1. When there ispositive potential at cathode terminal K1, MOS transistor T1, with itsintegrated inverse diode D6, is in the blocking mode and capacitor C1may charge itself via diode D3 and resistor R5. The voltage present atcapacitor C1 is used for supplying the further components of therectifier circuit.

However, if the electric potential at cathode terminal K1 is morenegative than the electric potential at anode terminal A1 of therectifier circuit, the gate-source voltage of MOS transistor T1 ispositive and higher than its threshold voltage. MOS transistor T1 isconductive under these conditions, a current flow having this currentdirection causing only a slight voltage drop.

If the electric potential at cathode terminal K1 of the rectifiercircuit is again more positive than the electric potential at anodeterminal A1 of the rectifier circuit, the gate-source voltage of MOStransistor T1 is less than its threshold voltage. MOS transistor T1blocks under these conditions. For this reason, the current flow throughMOS transistor T1 is only very slight.

If the electric potential at cathode terminal K1 of the rectifiercircuit is more positive than the electric potential at anode terminalA1 of the rectifier circuit and this potential difference exceeds avalue set by Zener diode D4, the input potential of the currentamplifier stage, which is made up of transistors T4 and T5, is raised.As a result, the gate-source voltage of MOS transistor T1 alsoincreases, and current flows between the drain and the source of MOStransistor T1. Under the given conditions, this current flow limits theelectric potential difference between cathode terminal K1 and anodeterminal A1 of the rectifier circuit to a predetermined value. Thisfeature of limiting the potential difference is a clamping voltage and,in special cases, forms a protection against overvoltages or forms aload dump protection.

In this case, the electric strength of MOSFET transistor T1 is designedin such a way that its drain-source breakdown voltage is substantiallyhigher than the clamping voltage of the circuit determined by clampingdiode D4. For example, at a clamping voltage of 22 V, a power MOSFETtransistor having a drain-source breakdown voltage of approximately 40 Vis utilized. During the clamping with the aid of diode D4, transistor T1is simultaneously operated at high voltages and currents. This isreferred to as operation in current saturation or also as the linearmode.

The linear mode is unstable, in particular, in modern MOSFET transistorswith their small cell structures. At high drain-source voltages and highdrain currents, the current tends to constrict at a point, which mayresult in the destruction of the component.

SUMMARY

According to the present invention, a rectifier circuit is provided,which includes a cathode terminal, an anode terminal and, between thecathode terminal and the anode terminal, an electronic circuit whichcontains at least one MOSFET transistor having an integrated inversediode, the drain-source breakdown voltage of the MOSFET transistoroperated in the avalanche mode corresponding to the clamping voltagebetween the cathode terminal and the anode terminal of the rectifiercircuit.

According to the present invention, it is provided that, instead of thepreviously used, active voltage clamping, a MOSFET transistor is used,whose drain-source breakdown voltage corresponds to the desired clampingvoltage. Since the property of the reduced drain-source breakdownvoltage is coupled to the reduction of the closing resistor, the methoddescribed here simultaneously results in the reduction of the power lossoccurring in the rectifier mode.

In addition, if the chip area of the power transistor is unchanged, theconducting state power losses in the rectifier mode are reduced and,additionally, a greater load capacity in the voltage clamping mode isachieved.

The MOSFET transistor may be a planar, vertical DMOSFET transistor. Atransistor in DMOS technology (double-diffused metal-oxidesemiconductor) is particularly well suited for this operation.

The structures of the MOSFET transistor are advantageously designed insuch a way that the power loss incurred in the avalanche breakdown isdistributed at least approximately uniformly over the active chip area.

The structures of the MOSFET transistor are advantageously designed insuch a way that an injection of charge carriers into a gate oxide of theMOSFET transistor is avoided.

The MOSFET transistor may be a trench MOS transistor. Since, accordingto the present invention, the avalanche mode is advantageously utilizedinstead of the linear mode, it is now possible to also utilize trenchtransistors having a small cell size.

According to the present invention, an electronic component forrectifying AC voltages, which includes at least one previously describedrectifier circuit, is provided. The same advantages and modifications aspreviously described apply.

According to the present invention, a generator for the voltage supplyof a motor vehicle is furthermore provided, the generator including atleast one previously described rectifier circuit and/or a previouslydescribed electronic component. The same advantages and modifications aspreviously described apply.

The method according to the present invention for operating a rectifiercircuit which contains a cathode terminal, an anode terminal and,between the cathode terminal and the anode terminal, at least one MOSFETtransistor having an integrated inverse diode, includes, generally, thefollowing steps:

-   -   selecting the drain-source breakdown voltage of the MOSFET        transistor in accordance with the clamping voltage between the        cathode terminal and the anode terminal; and    -   operating the MOSFET transistor in the avalanche mode.

The same advantages and modifications as previously described apply.

Advantageous refinements of the present invention are describeddescribed in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are described in greaterdetail with reference to the figures and the description below.

FIG. 1 shows a rectifier circuit from the related art.

FIG. 2 shows a rectifier circuit according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

A rectifier circuit 1 including an electronic circuit 2, which issituated between a cathode terminal K1 and an anode terminal A1, isrepresented in FIG. 2. In rectifier circuit 1, a power transistorcomposed of T1 and D6 is operated in avalanche breakdown. Powertransistor T1/D6 has a drain-source breakdown voltage which correspondsto the desired clamping voltage. In applications in motor vehicles, forexample, clamping voltages are in the range from 20 to 30 or 40 volts.

As compared to FIG. 1, Zener diode D4 and resistor R6 are thereforeomitted. For the sake of clarity, repetitions are dispensed with hereand only the differences from FIG. 1 are explained.

In FIG. 1, the breakdown voltage of the transistor, at approximately 40V, is high as compared to voltages of the utilization or application,and so an active activation of the transistor is required for theclamping. According to FIG. 2, however, the breakdown voltage, atapproximately 20 V, is so low as compared to the voltages of theapplication that transistor T1 or diode D6 automatically clamps thevoltage peaks. Diode D6 is represented here as a Zener diode in order toshow that diode D6 functions as a Zener diode due to the avalanche mode.

The clamping takes place generally in two states: in one state, duringshort transient processes of the kind caused, for example, by theinductive connection of a generator to a vehicle electrical system of amotor vehicle; in the other state, during long transient processes ofthe kind which occur, for example, during a load dump.

In order to implement the circuit, the technology and transistor T1 areselected or dimensioned in such a way that the clamping voltage may beset by transistor T1. This means that the drain-source breakdown voltageof transistor T1 corresponds to the desired clamping voltage.

For power transistor T1/D6, a MOSFET in planar, vertical DMOS technology(double-diffused metal-oxide semiconductor), for example, may beutilized.

The on-resistance Ron of MOSFETs depends on its electric strength or onits breakdown voltage BVdss. The on-resistance Ron increasesoverproportionally with the blocking voltage. For vertical DMOStransistors, Ron increases proportionally with BVdss^(2,5). As a result,due to the measure according to the present invention, the on-resistanceof a synchronous rectifier according to FIG. 2 is advantageously reducedas compared to the original arrangement according to FIG. 1.

The operation in the avalanche mode also allows for the use of modern,avalanche-resistant MOSFET transistors having a small cell size. Forexample, transistors in trench MOSFET technology may now also beutilized. Trench MOS transistors are not particularly well suited foroperation in the linear mode, due to their small structural size andhigh slope. The use of modern transistors in a circuit according to FIG.1 is therefore extremely limited. If the avalanche mode is utilizedinstead of the linear mode, transistors having a small cell geometrysuch as, for example, trench transistors, may also be utilized.

What is claimed is:
 1. A rectifier circuit, comprising: a cathodeterminal; an anode terminal; an electronic circuit between the cathodeterminal and the anode terminal, the electronic circuit including atleast one MOSFET transistor having an integrated inverse diode, theelectronic circuit being configured to operate the MOSFET transistor inan avalanche mode of the MOSFET transistor, the electronic circuitconfigured to rectify an alternating voltage applied between the cathodeterminal and the anode terminal; wherein a drain-source breakdownvoltage of the MOSFET transistor operated in the avalanche modecorresponds to a clamping voltage between the cathode terminal and theanode terminal of the rectifier circuit, wherein the MOSFET transistorclamps voltages of the applied alternating voltage at the drain-sourcebreakdown voltage of the MOSFET.
 2. The rectifier circuit as recited inclaim 1, wherein the MOSFET transistor is a planar, vertical DMOSFETtransistor.
 3. The rectifier circuit as recited in claim 1, wherein theMOSFET transistor is a trench MOS transistor.
 4. The rectifier circuitas recited in claim 1, wherein the MOSFET transistor is designed in sucha way that a power loss incurred in the avalanche breakdown isdistributed at least approximately uniformly over the active chip area.5. The rectifier circuit as recited in claim 1, wherein the MOSFETtransistor is designed in such a way that an injection of chargecarriers into a gate oxide of the MOSFET transistor is avoided.
 6. Anelectronic component for rectification of AC voltages, the electroniccomponent including at least one rectifier circuit comprising: a cathodeterminal; an anode terminal; an electronic circuit between the cathodeterminal and the anode terminal, the electronic circuit including atleast one MOSFET transistor having an integrated inverse diode, theelectronic circuit being configured to operate the MOSFET transistor inavalanche mode of the MOSFET transistor, the electronic circuitconfigured to rectify an alternating voltage applied between the cathodeterminal and the anode terminal; wherein a drain-source breakdownvoltage of the MOSFET transistor operated in the avalanche modecorresponds to a clamping voltage between the cathode terminal and theanode terminal of the rectifier circuit, wherein the MOSFET transistorclamps voltages of the applied alternating voltage at the drain-sourcebreakdown voltage of the MOSFET.
 7. A generator for the voltage supplyof a motor vehicle, which includes at least one rectifier circuitcomprising: a cathode terminal; an anode terminal; an electronic circuitbetween the cathode terminal and the anode terminal, the electroniccircuit including at least one MOSFET transistor having an integratedinverse diode, the electronic circuit being configured to operate theMOSFET transistor in an avalanche mode of the MOSFET transistor, theelectronic circuit configured to rectify an alternating voltage appliedbetween the cathode terminal and the anode terminal; wherein adrain-source breakdown voltage of the MOSFET transistor operated in theavalanche mode corresponds to a clamping voltage between the cathodeterminal and the anode terminal of the rectifier circuit, wherein theMOSFET transistor clamps voltages of the applied alternating voltage atthe drain-source breakdown voltage of the MOSFET.